1. Field of the Invention
The present invention relates to a thin-film semiconductor device used for an areal-pressure-distribution detector or the like, and more particularly, relates to an electrode structure of a semiconductor device.
2. Description of the Related Art
As disclosed in Japanese Unexamined Patent Publication No. 6-288846, matrix-type areal-pressure-distribution detectors are known in which semiconductor devices and others are used. FIG. 8 schematically shows an example of a conventional fingerprint sensor to which such an areal-pressure distribution detector is applied. This fingerprint sensor comprises a semiconductor substrate 201 such as a silicon substrate, and an integrated detecting member 202 formed on the substrate according to a semiconductor-manufacturing process. A flexible film 203 is further laminated on the semiconductor substrate 201. This film 203 is made of, for example, polyester or polyamide, and a conductive film is formed under the film according to vapor deposition or the like. Among the bipolar transistors constituting the detecting member 202, only emitter electrodes are illustrated in FIG. 8. The emitter electrodes are separated from each other by a silicon oxide film 204. For fingerprint detection, a subject finger 205 is put and slightly pressed on the film 203. At the sites where cutaneous ridges touch, the conductive film formed under the flexible film 203 comes into contact with emitter electrodes of the transistors constituting the detecting member 202 situated under the conductive film. Here, the conductive film formed under the flexible film 203 is grounded. As a result, the emitter electrodes are earthed through the conductive film. The thus-input signal voltages are read by transistors, respectively, and the areal-pressure distribution is determined to detect a fingerprint. Incidentally, an anisotropic conductive film which has conductivity only in the direction of the film thickness may be used instead of the flexible film 203 to which the conductive film is deposited.
Hitherto, areal-pressure distribution detectors have been formed with bulk-type semiconductor devices each comprising a silicon wafer and integrated transistors formed thereon. Such a silicon wafer is, however, expensive, and requires careful handling since it is readily mechanically broken by a stress added from outside.